Dual loop heat pumps or refrigeration systems which utilize a linear motion free-piston expansion-compression device are known in the art. Such devices utilize a single working fluid in each loop of the system having a power loop which operates on a Rankine cycle and a refrigeration or heat pump loop which operates on a vapor compression cycle. One of the disadvantages of these prior art systems is that the operational efficiency thereof is poor because the linear momentum and temporary storage of kinetic energy in the free piston assembly is not utilized to compress the working fluid in the refrigeration or heat pump loop. This has resulted in such prior art systems being economically unfeasible. Further, these systems require a relatively high operating temperature and pressure for the power loop working fluid, thereby limiting the operating range.
Rotary heat driven compressors and/or engines do not use conventional pistons for compression. Instead, they work on rotary motion. When once started, the rotor turns constantly in one direction until turned off. There is no loss of efficiency due to piston action, i.e. pistons which move in one direction, stop, reverse direction, move and then stop and reverse again.